01 June 2012

The Planets at 50

The metallic dragonfly known as Mariner 2, a derivative of the then-struggling lunar Ranger series and modified for interplanetary cruise and launched in August 1962 toward the planet Venus. With a wingspan at just over 5 feet (almost 2 meters), this dragonfly would have outsized even its Jurrasic cousins.

2012 is an important year for celebration, at least in the semi-arbitrary sense of human numerology. The fact that we have ten digits, count our personal anniversaries on the basis of seasonal revolutions of the Earth about the Sun and measure our life spans in decades dictates that decadal anniversaries are regarded of some importance, and century anniversaries in particular. August 2012 marks the 50th anniversary of the launch of the first successful interplanetary explorer, Mariner 2, which lifted off from Cape Canavaral in August 1962 and encountered Venus in December that year. This marked the first successful interplanetary* exploration in human history. This event also marked what can be considered the true beginning of the current revolution in our understanding of our Solar neighborhood, including fundamental revelations about how our own planet came into being and evolved. With this in mind and the imminent Venus transit on June 5th, it's a good time to look back on that half century and see what we have accomplished and what we have learned, scientifically and as a species.

To celebrate that achievement, I will be posting an extended discussion of those 50 years, the first pioneering voyages, the major milestones, where we have been and what we have learned from it all. The plan is to publish these articles in a series of 5 or 6 posts over the next few weeks. It all begins today with an assessment of where we stood 50 long years ago on the eve of launch . . .

*Planetary in this case referring to beyond the twin Earth-Moon system, and is focused on the "debris" currently orbiting the Sun (as such Sun-focused exploration will not be addressed).

1958-1962: In The Beginning . . .

Today we have an international armada of spacecraft (below) orbiting or on their way to (at last count) one comet, three dwarf planets (in both the Kuiper and Asteroid Belts), and to every planet except Uranus and Neptune (hey NASA, ice giants are key members of the Solar System too!). We have in the past decade or two also visited 4 other comets, at least a dozen asteroids, and had a virtual armada in orbit or on the surface of Mars since 1997. That is indeed an impressive state of affairs, considering that as recently as 1988 we had but two interplanetary spacecraft at all beyond the Earth-Moon system (that being Voyager 1 & 2). But in 1962 we considered ourselves fortunate whenever vehicles made it into Earth orbit, and even then surviving as a functioning robot until planetfall was an eventful ride. It is still not a risk-free endeavor as the Phobos-Grunt, Mars Polar Lander and Akatsuki experiences remind us.

Olaf Frohn's chart showing the fleet of interplanetary spacecraft currently in operation (as of April 2012). Courtesy of Emily Lawdawalla's blog. The chart would be empty in Summer 1962.

IGY and the Space Race

It is useful to remember the context in which all of this started. Post World War II, the United States and Soviet Union were engaged in the Cold War, with its subsidiary competitions the Arms Race, Missile Race (or Gap), and of course the Space Race. Beginning in 1957 it had suddenly become very important for national prestige to be the first to do something or go somewhere in space. The Space genie had been let out of the bottle so to speak in the late 1950's, when plans were put in motion to finally launch the orbiting satellites long dreamt of by novelists, artists, and scientists alike. The impetus to do so in earnest was the Int'l Geophysical Year (IGY), a cooperative scientific agenda or program focused on investigating Earth geophysics, including its interior and its interactions with the space environment. This program and the prestige associated with it (which was quote pronounced for its time) motivated the superpowers to push their advancing rocket technology to place a satellite into orbit, preferably with science instruments aboard. Even the official emblem for IGY (below) featured a then-nonexistent Earth-orbiting satellite, symbolizing the scientific hopes attached to space. While the Soviets reached orbit first, it was the americans who did so first with instruments dedicated to IGY, leading to fundamental and radical discoveries about the radiation belts and the solar wind, among other things. These were among the first real indications of the vast unknowns awaiting us in our own solar neighborhood.

The lunar landing initiative launched by Kennedy in 1961 focused our early efforts to understanding the Moon in preparation for Apollo, at least for the 1960's. The Moon's close proximity and relative ease of access (despite the low rate of early success) also made it the obvious first target. Despite this, NASA's charter (http://history.nasa.gov/spaceact.html) was specifically written in 1958 to say, among other things, "(c) The aeronautical and space activities of the United States shall be conducted so as to contribute materially to one or more of the following objectives: (1) The expansion of human knowledge of phenomena in the atmosphere and space;". The fact that this objective is listed first may be regarded as more than a coincidence, but it is a broadly defined objective, and our planetary neighborhood has been a major component of NASA's exploration program since inception.

Despite the lunar focus, Venus and Mars remained on the menu, and the first realistic opportunity arose during the 1961 conjunction with Venus. There have always been strong academic communities genuinely interested in science and outer space and at least in the US of A, where control over space programs was handed over to the civilian sector, they have been allowed to at least partially drive the planning and design of much of our planetary program. The planets were obvious and convenient targets as the outer space frontier opened up, the race to reach them first was on. The Soviets launched the first missions to both Venus and Mars that year but each attempt failed either during launch or from in-flight failures long before reaching their targets. Both sides would have to wait for 1962 to try again.

1962: STATE OF THE SOLAR SYSTEM

Before we look at the first flight to Venus and how far we've come generally, let's review where we stood in the summer of 1962.

Since the heady first discoveries of Galileo and Cassini and others (the men, not the machines), the Solar System had become something of a backwater, relegated in the early 20th century to off peak hours at the telescope in favor of the more glamorous nebular and galactic branches of astronomy. Planets and especially asteroids were "vermin of the sky", interfering with more "profitable" observing. In the decades leading up to the Space Age, planetary observations were limited to photometric studies or similar endeavors, as true spectroscopy was still in its infancy and adaptive optics were a mere concept if that. Our nearest neighbors in space, Venus and Mars, were fuzzy tennis balls or enigmatic spheres with tantalizing but hopelessly cryptic dusky markings. There just wasn't much to say about our planetary neighbors.

Literature on the planets in the late 1950's had a quality that reminds one of the shrouded mysteries of the North American continent evoked by the sketchy and grossly incomplete (and often inaccurate) maps of the 16th and 17th century. Together with the tall tales coming back from early explorers, the lure of that (not quite) virgin land mass was irresistible for some. Similarly for the unexplored and largely unknown Solar System visible in our own back yard as bright lights in the sky. Articles in Collier's and books by Willy Ley and Arthur Clarke, among others, often accompanied by illustrations by Chesley Bonestell and Ludek Pesek, among others, evoked alien landscapes constrained only by the imagination and by a few meager (and sometimes erroneous) facts.

Books on the Solar System in 1962 could be 100 pages long and still be complete, reflecting how little was known about the Solar System and its members. Even plate tectonics did not fully exist as yet as a coherent theory of how our own planet works (the IGY contributed fundamentally to this but it would be nearly a decade before all the pieces could be put together to understand the big picture). Indeed, large section of these texts, especially popular books, were given over to speculations. Much of that speculation focused to Mars, the nearest body for which we could resolve any markings, and hence the one believed tobe most Earth-like and most rife with possibilities. We were still uncertain of what the atmosphere of Mars was made of or how dense it was, however, but those cryptic and changing dark markings gave seed to many an interesting idea (more on that later).

Cover of the book "All about the Planets," published in 1960 and resident of many a youngster's book shelf in the early 1960's, including my own. The serene cover artwork portrays a Solar System of static order and tranquility, yet one shrouded in mystery and wonder, not unlike the North American continent in the 16th and 17th centuries.

In 1962, the Solar System was a static, well-ordered place where, aside from a stray comet, not much happened, a view in stark contrast to our present understanding (which I will describe in some detail next month). It was thought "there may or may not be planets beyond Pluto." "Certainly we shall have stronger evidence in a few years and then be able to say whether the changing seasonal colors on Mars are due to vegetational responses, or are just the result of sand storms." A paragraph was sufficient to describe all we knew then about the amazing planet-like Galilean satellites of Jupiter. It was believed even back then that the inner two, Io and Europa, were Moon-like but that the outer two Ganymede and Callisto had significant quantities of ices, but other than the unusual brightness of their surfaces, little else was known. The size of Neptune's largest moon, Triton, could not be reliably ascertained until 1989, when Voyager 2 observed the disk of this frigid orb directly.

Even some of the most basic properties of neighboring planets, such as the rotation periods of Venus and Mercury, were incorrectly estimated. The innermost planet was described in one book as "a bare ball of rock and metal, with 'light areas" and "dark areas," none of which could be reliably correlated from one observer to another or one apparition to another. Such were the mysteries that abounded in the cryptic void of hard information. Such were the uncharted terrains described in books a young lad would read in the dawning years of the space age.

Prelude to Venus

So then, on the eve of the launches of Mariner 1 and 2, what did we think was going on at Venus? Only slowly did the veil lift from the Mother of Loves, brightest star of the evening and morning skies. Little more than a dusky bright white disc for centuries, its atmosphere was not confirmed until the transit of Venus across the Sun in 1761. Indeed, it was these transits that first indicated the similarity in size between the Earth and Venus, giving rise to speculations about twin planets and all that that loaded comparison might suggest for life on our nearest neighbor. But it would require another two ceturies for more secrets to be revealed. CO2, the first atmospheric component to be reveled, was not confirmed until 1932. Microwave observations in the 1950's hinted at a warm surface, possibly several hundred °K. The cloud composition was still uncertain, as was the rotation period (finally pinned down by Earth-based radar observations beginning in 1962).

One nightmarish vision of a windswept Saharan Venus.

Even though the composition of the clouds was not known till much later, the dense cloud cover gave rise to visions of dank steamy swamps and coal beds across Venus, not unlike conditions in the Jurassic on its twin, Earth. By the time Patrick Moore wrote his book on "Venus" in 1958, that view was considered unlikely, and a hot dry Sahara-like Venus was gaining some popularity. The thick carbon-dioxide rich atmosphere gave rise to informed speculations about trapped heat and "greenhouse effects" on Venus (and subsequently on Earth) championed by Carl Sagan in some of his first scientific work. But even Sir Patrick, in his otherwise fine book, gave some final speculative thoughts to life on Venus, concluding that a near Cambrian Venus, with primitive life forms slowly developing in a warm oxygen-poor atmosphere, was possible, wistfully awaiting new knowledge. Confirmation of life-threatening hot surface temperatures would have to wait for close examination by spacecraft, as would the presence or absence of radiation belts and a shielding magnetic field. The stage was set for the Mariners . . .

1 comment:

"Soon enough there will appear new and amazing animals from Mars or Venus in our zoos. Of course, we will be ogling them and slapping our sides, but we have been waiting for them a long time, andwe are prepared for their appearance. We would be much more astounded and disappointed if there would not be any such animal or if they would be like our cats and dogs." (Arkadi and Boris Strugatsky. Monday begins on Saturday; 1966)

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NOTES ABOUT THE DATA

These brief notes are posted to help viewers understand the nature of the topographic data. Voyager, Galileo and Cassini carried imaging cameras but not altimeters. Topography is instead generated using stereo images or low-Sun images (which can be used to calculate slopes and heights). Neither method is perfect and often, as is the case for Miranda, individual stereo pairs must be constructed and then stitched back together to form a global or partial topographic map. This means that the elevations shown are not precise with respect to the center of the body. Height values derived are accurate however with respect to local features. For example, we know the steep cliff on Miranda is about 10 km high top to base but we do not know how high it is with respect to the mean "sea level" on Miranda. This cannot be determined until we return to these places.I will post additional information on the data over the next few days.

Inquiries for the scientific use of the original digital elevation data should be forwarded to schenk@lpi.usra.edu.